The present invention relates to a railway cross-tie of molded and bonded lignocellulosic material internally reinforced against positive and negative bending stresses expected from train movements over a railway track. Most conventional railway crossties used in this country today are lumber beams, approximately 7 inches thick by 9 inches wide by 81/2 or 9 feet long, that have been cut from sections of live tree trunks selected to be free from soft or decayed spots, shakes, worm holes, and other imperfections. Before being placed into service as crossties, these beams are treated with creosote, an oily liquid preservative, to protect them against the effects of exposure to the elements.
The major disadvantages of using lumber beams for railway crossties are the ever-increasing costs of raw lumber, the difficulty of applying creosote with sufficient penetration to prevent rapid deterioration of the beams, and the need continually to replace and dispose of those beams that are split, rotted and worn. As an example of this latter problem it has been reported that the Santa Fe Railroad alone uses approximately 1.6 million lumber crossties annually. A few of these ties are subsequently sold to farmers and ranchers along the railway right-of-way, but most must be buried underground as current ecological considerations prohibit their being burned in the open or left along the right-of-way for extended periods of time.
Previous attempts have been made to develop a substitute for the conventional wooden crosstie, such as by manufacturing crossties from synthetic resins as shown in Groff U.S. Pat. No. 3,289,940, or from concrete, steel or thin particle board sheets made from recycled ties or other lignocellulosic materials and laminated together. These attempts have not been successful, however, due to the higher costs of the substitute crossties, lack of sufficient strength and durability in some cases to withstand the cyclic bending and vibratory loads peculiar to crossties, lack of hardness and undue susceptibility to tie plate wear, non-adaptability of such substitute materials to the use of conventional rail-fastening spikes, inability to hold such spikes in place under normal service, and, in the case of the metal substitutes, electrical conductivity of the material employed. (Since the metal rails fastened to the ties to form the railway are also often utilized as electrical conductors for the railway signal system, it is imperative that the crossties be electrically nonconductive so not to create an electrical circuit between the rails and thereby disrupt the signalling system.)
One approach to overcoming the aforementioned problems of conventional railway ties produced from raw lumber, and the aforementioned types of substitute crossties, has achieved success by the use of a mixture of comminuted lignocellulosic material bonded together and molded in the form of a highly densified, thick monolithic beam, having the dimensions of a conventional lumber railway crosstie, around a plurality of elongate metal reinforcing rods, as described in my copending patent application entitled "Reinforced Molded Crosstie and Method for Making Same", Ser. No. 588,786, filed June 20, 1975, herein incorporated in its entirety by reference. Such highly densified synthetic crossties provide an economical, electrically nonconductive substitute for the conventional wooden railway crosstie and have good resistance to decay, stress and wear and excellent spike-holding qualities. The bond between the metal reinforcing rods and the lignocellulosic material is considerably enhanced by lateral protrusions attached along the rods to prevent slippage. However the metal used to produce the elongate reinforcing members and the lateral protrusions add a certain amount to the cost of production which would be desirable to eliminate if possible. Also, the positioning of the spikes used to fasten the rails to the ties is somewhat critical if interference with the signalling system is to be avoided since they cannot touch the conductive metal reinforcing members.
Another approach to overcoming the problems of conventional railway crossties is suggested in Collins et al U.S. Pat. No. 3,908,902 wherein railway ties are molded from a mixture of comminuted material and a binder, and slabs of wood are included in the mix for reinforcement. Although the use of such wood slabs may tend to increase the strength of such crossties and reduce the reinforcing cost and the problem of interference with the signalling system, the Collins et al ties are produced at the relatively low pressure of only 300-800 psi which would indicate low resistance to stress, vibration and wear and low-spike holding qualities. Higher pressure would crush most common wood reinforcing material during the tie manufacturing process, rendering it ineffective. Also, the arbitrary placement of wooden slabs in such a tie as reinforcing material may fail to maximize the tie's resistance to the particular types of bending stresses to which railway crossties are typically subjected.
Accordingly, a need exists for an economical reinforced molded railway tie utilizing lignocellulosic particles which has excellent resistance to decay, stress and wear and excellent spike-holding qualities, and utilizes a reinforcing material which can withstand high compressive force without crushing, is less expensive than metal and produces a molded crosstie which is stronger than that produced by metal reinforcing. Also, it is desirable to reduce the criticality of the placement of reinforcing members in such a tie with respect to the spikes while utilizing the placement of the reinforcing members to maximize the tie's resistance to special tie bending stresses.